The present invention relates to circuitry for handling electrical musical signals and more particularly concerns electrical musical instrument amplifiers that enable the musician to provide a readily-selected amount of distortion and/or harmonics in the sound of his music.
Different musicians will differ in taste and requirement for harmonic content on the sound created. Some musicians in general prefer a relatively clean or undistorted sound having a relatively low harmonic content and distortion, whereas others typically prefer high levels of both harmonics and distortion. Further, the amount of harmonics and distortion that may be desired will vary with selections being played by a particular musician. Various types of tone-modifying circuits have been employed over the past years in electrical-musical instruments for providing different musical effects such as wah-wah, tremulo, reverberation, fuzz and distortion. Such circuits are exemplified by U.S. Pat. Nos. 3,213,181 to Snoddy et al.; 3,530,224 to Plunkett et al.; 3,544,694 to Freeman; 3,553,338 to Holman; 3,663,735 to Evans; 3,749,809 to Niinomi.
Throughout this application, the terms "distortion" and "harmonics" are used interchangeably, as the effects known as distortion and/or high-level harmonics are substantially identical for the purposes of this invention.
Where distortion is required according to the selection of the musician, a separate distortion circuit or channel has been provided in the past. When the distortion or special effects are required, the output of this channel is switched to the sound transducer or loudspeaker output. However, the prior systems suffer from a significant defect in that the amount of distortion is not readily selectable without significantly changing the apparent average sound level of the output. Accordingly, in instruments of the prior art, it is necessary to operate two controls simultaneously in order to vary the amount of desired distortion or harmonics without changing the apparent loudness of the output. For example, in order to increase the amount of distortion in prior systems, the musician would operate a distortion channel volume control to increase the level of the signal in this channel and thus increase the amount of distortion, and at the same time, would adjust a master volume control to decrease the sound level output.
Further, once having selected the particular amount of distortion, it is often desirable to change the sound output from a distorted version to a clean or undistorted version in the course of a particular musical selection. Circuits of the prior art are not readily adaptable to such controlled switching between distorted and clean sounds and often introduce noise such as audible clicks that are attendant upon switching. The above-mentioned patent to Evans describes an arrangement employing ganged switching devices at the ouput of each of a pair of channels for choosing one or the other, but this arrangement requires relatively complex additional circuitry and simultaneous control of several switches.
Accordingly, it is an object of the present invention to provide a selective distortion circuit for an electrical musical instrument that substantially eliminates or minimizes the above-mentioned problems of the prior art and enables the combining of a signal having a selected amount of distortion or harmonic content with a clean signal in a desired degree.